A critical review of the current design guidelines for footbridges: with emphasis on the design for jogging forces

Master Thesis


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University of Cape Town

New materials and the modern trend of designing slender, lightweight footbridges with longer spans have resulted in bridges with lower inherent structural damping and natural frequency in the range of pedestrian-induced dynamic loading from activities such as walking, running and jogging. This has lead to a number of recent footbridges suffering from excessive vertical or lateral vibrations necessitating retrofitting, usually at high additional costs ((Butz, 2008; Sun and Yuan, 2008)). One of the most important aspects of the design of modern footbridges for dynamic forces is the development of a reliable model of both the structure and the human induced loads applied to it. However, the current design codes and design procedures are either outdated or very limited with regards to the type of footbridge and pedestrian loading they consider. There is a “lack of commonly accepted models for walking, running and jumping” loads (Occhiuzzi et al., 2008), and the majority of the research that has been done and human-induced loading models that are available only look at the vertical component of the walking load. Research done by Keller et al. (1996) found that slow jogging can cause vertical forces up to 1.6 times greater than those caused by walking at the same speed or running at higher speeds. However, of all the codes of practice reviewed in this thesis only the Sétra Guide gives an indication of how to model the vertical component of a person running using either the Semi-Sinusoidal method or the Fourier method. Occhiuzzi et al. (2008) proposed a third method, the Analytical method, for modelling the vertical component of the jogging load. This thesis extends these three jogging load models to include the lateral and longitudinal component of the jogging force and to account for multiple people. The vertical forces obtained using these jogging load models were compared with those measured by a person running at various speeds on an instrumented treadmill. The comparison showed that for a contact period of 75 of the running period all three jogging load models give a reasonable approximation of the actual vertical jogging forces.

Includes bibliographical references.